Decoded Genome May Help Tortoise Win Survival Race

(CN) – A “slow and steady” adaptation to evolving hazards will not save the Mojave Desert tortoise from extinction, and to protect the endangered iconic species researchers have decoded the reptile’s genome to identify specific genes that will guide conservation efforts and improve its likelihood of survival.

Their findings appear Wednesday in the journal PLOS ONE.

“There is more and more development across deserts, as well as a surge of renewable energy development,” said Todd Esque, a research ecologist and tortoise expert with the U.S. Geological Survey who was not involved in the study. “Highways and power lines disturb the tortoise habitat. We are also considering impacts to tortoise habitat from changes across the landscape.

“And, in the last 100 years, we’ve had invasive grasses come in with livestock, probably mostly accidental. Red brome and Mediterranean grass are the two primary invasive grasses we have here. A diet of primarily red brome is really a bad diet for little tortoises and their survivorship is much lower.”

Researchers and government agencies have monitored tortoise populations in the Southwest for more than two decades. During that period, the Mojave Desert tortoise population has declined significantly in habitats across Arizona, Utah, Nevada and California. The species is listed as ‘threatened’ under the U.S. Endangered Species Act.

The genome is a valuable tool for conservation efforts since the population is suffering from a serious respiratory disease, according to lead investigator Marc Tollis, a postdoctoral researcher at Arizona State University. Scientists are unsure of the cause of the disease or what makes tortoises susceptible to it.

“We don’t know how the tortoise is handling the fact that it’s also being threatened by an upper respiratory disease,” said Tollis. “Decoding this genome will help us catalog which tortoise genes are evolving quickly enough to help them overcome this threat.”

Tollis and the paper’s senior author, ASU professor Kenro Kusumi, obtained the genetic data for a specific tortoise specimen and assembled and annotated the genome – revealing the evolutionary history of tortoises.

“Decoding a genome has gotten technically a lot easier,” Kusumi said. “What’s challenging now is decoding the information in the tortoise genome. We can use clues from similarities with the mouse and human genomes. Finding the proverbial ‘needle in the haystack’ would be to identify the genes that direct the immune response to infectious disease, as well as the ability to survive the harsh conditions of the Mojave Desert.”

Kusumi added it’s important for the team to identify areas with higher tortoise diversity across its geographic range in order to preserve tortoise populations that may be more able to respond to unknown challenges in the future.

Greer Dolby, study co-author and ASU postdoctoral associate, is also examining the genetic differences between the Mojave Desert tortoise and its sister species, the Sonoran Desert tortoise.

“My hope is that this study will enable other agencies to ask new questions, questions they would not have been able to ask without this research,” Dolby said. “For instance, ‘What immune genes do tortoises have to fight pathogens? How does their immune system function in an environment with lots of threats? And, how might a changing environment impact this?’ These are important questions to answer in managing the species.

“Now, we can begin investigating.”

Mojave Desert tortoises hibernate from mid-October through November, only leaving their burrows to drink water when it rains. They become active again as the weather warms in March, and mate during the spring. Females will lay a clutch of eggs up to three times a year, depending on the weather.

Desert tortoises can live up to 50 years in the wild, with lifespans averaging 30 to 50 years. Tortoises in captivity can live as long as 100 years.